This project is a collaborative effort between the Boston VA Medical Center (VAMC) and the Mallory Institute of Pathology (MIP). The long term objectives are to determine how repeated exposures to aerosolized antigens make guinea pig lung mast cells nonresponsive (NR) to sensitization either actively or passively and to determine if this NR state can be induced in other animals and man to prevent allergen mediated asthma. In vitro studies with chopped lungs show that normal lungs can be passively sensitized to release histamine on antigen challenge whereas lungs from sensitive and NR animals cannot. Pretreatment of the NR mast cells with acid dissociates a putative blocking factor or somehow exposes IgG1a receptors so that the mast cells can be passively sensitized for antigen induced histamine release. The eluate from the acid stripping does not prevent passive sensitization of skin or chopped lung. The specific aims of this application are to (1) Develop a functional assay for the putative blocking factor using milder methods of dissociation to prevent its denaturation, (2) Determine whether immune complexes of IgG1, IgG2, and IgA inhibit passive sensitization of skin and chopped lung, (3) Determine the immunoglobulins present on the surface of the normal, sensitive and NR lung mast cells and determine if these immunoglobulins are complexed with antigen using the immunoperoxidase method with tissue sections. If these methods fail to identify an immunoglobulin or immune complex to be responsible for the NR then mast cells will be purified and treated with acid stripping. The protein differences in the eluates from normal, sensitive and NR mast cells will be characterized as to electrophoretic mobility and molecular weight by SDS polyacrylamide gel electrophoresis. The different proteins will be removed from the gels and used for immunogens in rabbits for specific antisera production.